The importance of regulatory evolution to the diversification of plant morphology is well recognized. Some of the best-understood examples also involve gene duplication and co-option of deeply conserved genetic modules. These instances underscore the important role of gene duplication events, which are associated with regulatory sub- and neofunctionalization. In particular, we discuss the relationship between regulatory evolution following gene duplication and the evolution of floral novelty. We also consider the repeated co-option of TCP gene family members to promote aspects of floral symmetry and the KNOX/ARP meristem genetic module to control compound leaf development. Both of these patterns of genetic convergence involve modifications of an ancestral regulatory network to create novel expression domains. Overall, such examples highlight the interdependence of the three processes--regulatory evolution, gene duplication and co-option--within the context of plant developmental evolution.